The author just does not care. It starts out full of promise, mystery, and neat if not typical characters, and decent story progression. It's a horror/mystery/shounen which was quite rare in the day, and somehow still isn't that popular even after Attack on Titan and Death Note. the premise is pretty interesting, the setting is interesting, but midway through it completely runs out of steam.
The broad strokes of it are that the author just seems to have run out of interest, or possibly ran out of ideas but it got popular enough the author felt the need to continue it. Chapters become 1/3rd of the length they once were and contain little to no meaningful plot development. There's a meaningless 20 chapter arc that you could literally skip and lose nothing. The author gives away so much of the plot by the halfway point, that they're forced to create meaningless shocking twists out of nothing.
There's a reason none of the other reviewers read this far, huh?
It was entertaining for a little while but there's honestly no reason for anyone to read this ever.